Trade winds travel from west to east across the United States and onto the Atlantic Ocean. As wind comes in contact with the land on the west coast, the land absorbs energy from the wind at low altitudes. As the terrain changes from hills and mountains on the west coast to flat lands across the Great Plains and back to hills on the east coast, winds at high levels periodically dip down into low-lying areas causing inconsistent wind conditions. Also, atmospheric and land conditions combine with thermals, such as those resulting from the sun rays reflecting off the land, to create high and low pressure areas, thereby further contributing to variations in wind speed and density.
These factors translate into increasingly significant site limitations for harvesting energy the farther eastward across the country one looks. As a result, most alternative energy projects, such as wind farms, are located on the west coast, to take advantage of the better wind quality at low altitudes typically found in those areas. Such sites are often unavoidably located in populated areas thereby being subject to high land costs and potential political resistance.
Once wind reaches the Atlantic Ocean, cool water and the absence of terrain allow the higher-level trade winds to drop to lower altitudes. Ocean water tends to absorb wind energy thereby creating waves. Wave heights and periods correlate well with wind speed whereby increases in average wind speed lead to increases in average wave height. As wave height increases, the volume of water making up that wave increases significantly. Due to the high density of water (64.2 lbs/ft3), waves could produce large quantities of energy, if harvested.
The present inventor has appreciated that, for many reasons, the ocean is an ideal location to exploit wind and wave energy. The best wind quality on the planet exists off shore. Ocean winds are steadier and stronger due to the absence of obstructions. As a result, waves are steady and predictable based on wind speed. To achieve energy conversion, the present inventor has further conceived of employing a mobile, open water based vessel and, in certain embodiments, of a plurality of such energy conversion vessels deployed in a flotilla.
Wave energy harvesting machines have been disclosed by the prior art. However, they are generally shore based and intended to generate electricity for sale through fixed power grids. Consequently, they are limited by, among other things, site limitations, the cost of ocean front property, and political issues such that enjoying profitability relative to traditional wave power systems is a challenge at best. In addition, since the best quality and most consistent wave activity occurs miles off shore, shore or near-shore sites with acceptable wave activity are relatively rare while acceptable deep ocean sites are almost unlimited. Furthermore, since the horizon is about 20 to 25 miles from land, offshore wave vessels beyond the horizon would not be visible from land thereby limiting or entirely obviating opposition.
Sites in or near ocean expanses employing wind turbine technology to generate electricity do exist. Many of these sights are located in the Baltic Sea. Denmark has aggressive plans to convert most of its energy generation to wind within the next decade. In the United States, locations have been suggested for wind turbine construction, including off the coast of Cape Cod in Massachusetts.
A major drawback with such projects is that they rely on land-based wind turbine technology in on-shore or marginally offshore applications. The turbine sites must be connected directly to a power grid to enable electrical energy to be sold. In addition, since they are close to land, such applications are impacted by the land effect conditions discussed above thereby further negatively affecting annual returns on investment. Still further, these systems are anchored directly to the ocean bottom and, therefore, require shallow ocean depths. For example, the Baltic Sea and Massachusetts coastal applications are possible since each has locations with depths of fifty feet or less. Yet another limitation on current wind farms is that they must be physically close to their demand to minimize transmission line losses. Consequently, most regions have a dearth of acceptable locations for wind energy generation.
With an appreciation for the foregoing, the present inventor has realized that systems for extracting energy from wind or waves can be ideally located in the open water as free floating structures. Site limitations, land costs, and political opposition are entirely or nearly entirely eliminated, and wind and wave conditions are ideal. Also, opportunities are presented for partnering with aquariums and museums for educational and marketing purposes and the like.
Nonetheless, operating in open water presents challenges. Exposure to harsh conditions demands that equipment be rugged and transportable to resist and avoid damage from storms and other sources. However, long distance water travel can be costly if not controlled. Furthermore, the potential for loss of communication requires robust backup systems and procedures.
One method for converting wave and wind energy to a readily usable form is electrolysis. Of course, the process of electrolysis to yield hydrogen gas and oxygen gas is well known in the art. For example, one will have reference to U.S. Pat. No. 4,457,816 to Galluzzo et al. for an Electrolysis Method for Decomposing Water into Hydrogen gas and Oxygen Gas; U.S. Pat. No. 5,858,185 to Christian for an Electrolytic Apparatus; and U.S. Pat. No. 5,143,025 to Munday for a Hydrogen and Oxygen System for Producing Fuel for Engines, each of which being incorporated herein by reference.
In considering the extraction of power from wind and waves, it will again be noted that there is a close correlation between wind speed and wave height. In approximately 1905, Rear Admiral Sir Francis Beaufort of the Royal Navy devised what is now termed the Beaufort scale, which continues to be a standard measurement. A uniform set of equivalents of Beaufort numbers, wind speed, and sea height was accepted in 1926 and revised slightly in 1946. In 1955, the World Meteorological Organization established a correspondence between the Beaufort Number, wind speed, and wave height. For instance, at Beaufort No. 3, winds are 7-10 knots, scattered whitecaps appear, and the seas are 2-3 feet in height. At Beaufort No. 5, wind velocity is 17-21 knots, some spray appears, and wave height is 6-8 feet.
It is well understood that other factors can cause wave heights to depart from the Beaufort scale at any particular wind speed. For instance, high waves may appear after a storm even in the absence of wind, particularly near the shore. Also, bottom conditions may cause wave heights to vary widely from the numbers established by Beaufort.
However, under normal conditions on the high seas, there will be a reasonably close correlation between wind speed and wave heights in accordance with the standards published by the World Meteorological Organization. Therefore, conditions that favor wind power generation over water, such as the wind farms operating in the Baltic Sea or proposed system for off the coast of Cape Cod, also favor use of wave power generation systems.
To more fully understand the potential for energy production in such wave energy conversion vessels, an understanding of annual wave activity is needed. Studies have indicated that wind patterns over the globe follow a “Weibull” statistical distribution. The shape and size of the distribution vary from site to site, but the overall distribution is the same. The distribution illustrated in FIG. 1 was extracted from a training publication from the Danish Wind Turbine Manufactures Association from wind recorded on location in the Baltic Sea where a large wind farm is currently in operation. It demonstrates the probability of achieving various wind speeds throughout the year. FIG. 1 indicates the percentage of time per year wind speeds achieve different speeds in miles per hour.
As FIG. 1 shows, the average wind will travel at approximately 11 miles per hour 10.8% of the time during a given year. Wind speeds will range from 0 to 48 MPH during a typical year. It is anticipated that from year to year the profile and length of the distribution will vary However, the distribution does provide an estimate to use in calculating future wind trends.
In the United States, the National Ocean and Atmospheric Administration (NOAA) monitors weather conditions off the coast of the United States. The National Data Buoy Center, which is part of NOAA, publishes historical data at given locations where buoys are anchored. Data from three locations were examined: Station 44008 located 54 nautical miles southeast of Nantucket, Mass., Station 44025 located in Long Island Sound 33 nautical miles south of Islip, N.Y., and Station 44011 located 170 nautical miles northeast of Hyannis, Mass. representing 9, 25, and 7 years of wind speeds, wave heights, and wave period data respectively.
The data indicates that the average and maximum wind speeds off the east coast of the United States is very similar to those in the Baltic Sea in that the annual average is about 12½ MPH and the daily maximums are in the high 40's to low 50's. Based on this similarity and for ease of calculation, the data in FIG. 1 depicting wind performance in the Baltic Sea will be used as the basis for the remaining calculations and discussion for wind distributions on the northeast coast of the United States. Based on the data generated from NOAA, the theoretical predictions set forth below are conservative since there is nearly a three mile per hour difference between the average wind speeds offshore of Cape Cod and the wind speeds in the Baltic Sea.
In FIG. 2, each type of line represents data from a different location near the New England coastline. The square points represent data from Station 44025, which is in the Long Island Sound 33 nautical miles south of Islip, N.Y., diamond points present data from Station 44008 is located 54 nautical miles southeast of Nantucket, and data from Station 44011, which is located 170 nautical miles north east of Hyannis, Mass. is indicated in triangles points. This data represents average wave heights at average wind speeds over many years. Average winds and wave heights change from month to month dependent on the season.
From the scatter plot of FIG. 2, one will realize that, the farther the buoys are located away from land and the deeper the water, the better the relationship is between wind speed and wave height and the higher the waves are for a given wind speed. For example, when the wind averages 12½ knots, the buoy located 33 nautical miles off Islip, N.Y., experiences waves that average about 4 feet while waves at the buoy disposed 170 nautical miles off the coast of Massachusetts are almost 7 feet at the same wind speed.
A statistical correlation can be determined between wind speed and wave height. This enables the prediction of wave heights and the calculation of expected power output in a wave conversion system of a given size. Given this correlation, wave heights follow the same “Weibull” distribution as does wind. The slope of that correlation will change based on the location at sea. Up to a given terminal point, the farther away from shore, the larger the average wave height. The terminal point can be considered an ideal site location since it yields the best possible annual wave action at the closest point to land.
The terminal point is likely dependent on the distance from land and water depth. For example, FIG. 2 suggests that the terminal point is disposed between 54 to 170 miles off the New England coast. In this case, a flotilla of energy conversion vessels could thus be well located operating about 70 to 90 miles east of Cape Cod.
Based on the correlation between wind speed and wave height, an estimate of wave distributions can be developed. For example, the buoy at Station 44008, which is located 54 nautical miles southeast of Nantucket, may be an advantageous location for wave energy generation. Data generated from that buoy indicates that, historically, waves generally vary in size from 0 to 11 meters or 0 to 36 feet in that location. Given the correlation between wind speed and wave heights, it is logical to substitute the same wind probability distribution across the range of annual wave heights. Eight foot waves occur 10% of the time during the year. Since this location has conservative wave action compared to the Gulf of Mexico, the West Coast, and the like, it will be used as a conservative estimate for calculating annual production outputs of the proposed system.
In addition, an analysis of wave period in seconds and wave height in feet was performed, on a random sampling of data generated in 2004 at Station 44008, which is again noted to be located 54 nautical miles southeast of Nantucket. FIG. 4 illustrates the strong, direct correlation between wave period and wave height. This information will facilitate the estimation of energy availability for a given linear length of ocean over time.
Where wave height is also correlated with wind speed, it can be concluded that wind speeds, wave heights, and wave periods tend to follow the same Weibull statistical distribution as illustrated in FIG. 3, which depicts a distribution of wave heights for corresponding wind speeds as presented in FIG. 1. From this conclusion, energy availability is predictable for given locations.
It will further be noted that the available energy in waves increases to the cube of an incremental increase in wave height. FIG. 5 illustrates wave height in feet on the X axis and the corresponding available power in kilowatts on the Y axis. The chart estimates the energy within a 20-foot wide span of one wave at various heights to simplify the calculations, again assuming a standard water density of 62.4 lbm/ft3. Wave power calculations are based on guidance outlined in the “Engineering and Design Coastal Engineering Manual” Part II describing Linear Wave Theory for Regular Waves, which was published by the Department of the Army, U.S. Army Corps of Engineers. That manual provides detailed calculations of wave power or wave energy flux.
Considering a location at sea 20 feet wide near Station 44008, the wave energy flux available in that space at recorded wave heights and periods as in FIG. 5 based on the percentage of time spent per year at that those energy levels as given in the Weibull distribution of FIG. 3 can be employed to estimate the annual accumulated energy curve for each wave height to develop the data in FIG. 6. It will be noted that high wave heights yield relatively little annual accumulated energy. Although the wave energy flux level, is high for large waves as shown in FIG. 5, the time spent per year at those levels is very low as shown in FIG. 3 such that the total energy accumulation is relatively low.
For example, FIG. 3 demonstrates that, most of the time, waves travel at approximately 8 feet approximately 10.8% of the time in a given year, which equals approximately 39.5 total days. FIG. 4 indicates that 8 foot waves occur every 5.5 seconds thereby yielding approximately 200 Kw per wave period as in FIG. 5. Based on the time spent at this wave height, the total accumulative power produced in a year would be approximately 191 Mw-hrs pursuant to FIG. 6.
Therefore, the total area under the curve in FIG. 6, which equals the total annual available power, for a 20 ft space near Station 44008 equals 6,094 Mw-hrs. Such calculations allow a determination of the return on capital investment that will drive a system to meet the Department of Energy's objective of $2 to $3 per kilogram of Hydrogen produced and to establish the rationale for pursuing this technology as discussed further below.
The absolute available energy in a volume of water can never be completely absorbed by a hydro-generator. Doing so would require that there be no exiting wave from the system. Assuming a system capable of absorbing at least 75% of the available energy in a given wave, however, one can estimate an expected energy production per year of 4.57 MW-hours or more.
In FIG. 7, the solid bars represent the available energy in a 20 foot space located 54 nautical miles southeast of Nantucket as shown in FIG. 5. The cross hatched bars represent the predicted 75% efficiency of the actual system.
In light of the extraordinary amount of energy available in waves, it will be appreciated that a system and method capable of extracting wave energy in an efficient and effective manner would represent a significant advance in the field of clean energy production.